Field of the Invention
The present disclosure relates to fingerprint identification, and in particular, to a ramp wave generation circuit, a digital-to-analog conversion circuit, and a fingerprint identification system.
Description of the Related Art
With the advancement of the security technologies, fingerprint identification gains more and more attractions among people, which is being more and more widely used in various fields. A capacitive fingerprint sensing system is typically formed by fingerprint sensing pixel circuits, which act as basic units of the fingerprint sensing system. The pixel circuit extracts a capacitance coupling signal of each pixel point, and then inputs the signal to another part of the fingerprint sensing system for amplification, analog-to-digital conversion, image splicing and operations alike, to finally extract valid fingerprint information. In related arts, the pixel array data is read generally in the following three manners: global analog-to-digital conversion, local analog-to-digital conversion or row-column analog-to-digital conversion. In the above three manners, a digital-to-analog conversion circuit always is used. However, in the digital-to-analog conversion circuit, a ramp wave generation circuit and a clock generator are simply subjected to the influence of process/voltage/temperature (PVT), and thus the performance of the fingerprint identification system deteriorates.